Electrochemical monitoring of aluminium corrosion in a cyclic atmospheric test chamber

Abstract

A three electrode probe, comprising an aluminium electrode of interest with surrounding graphite half rings, has been employed to study the corrosion behaviour of aluminium in an atmospheric test chamber, using a mixed salt spray with wet/dry cycling. The potential response of the probe reveals four distinct regions associated with initial wetting, the presence of a continuous electrolyte film, and initial and final drying. Understanding of the potential response, in terms of the corrosion behaviour of aluminium, is assisted by the use of intermittent polarization, whereby aluminium is transiently connected to one graphite electrode. Thus, localized corrosion initiates in the misting periods with enhanced corrosion in the early stages of electrolyte solution concentration through drying. Development of corrosion products in the concentrating. electrolyte solution probably hinders further corrosion at such sites. On the other hand, with increased times of exposure in the cabinet, the general development of corrosion products assists trapping of electrolyte solution, maintaining the surface wet, with continued corrosion activity. Quantification of the corrosion rate of aluminium over the period of exposure is not possible, largely due to localized corrosion beneath electrolyte droplets in the presence of a discontinuous electrolyte solution film. However, the probe monitors sensitively the various regions prevailing in the atmospheric test chamber.